1988 FL freightliner air conditioning q1

workshoprat92 · Aug 27, 2021

I have a 1988 Freightliner FLC. This weekend I am going to be changing the expansion valve, receiver dryer and the trinary switch. Also I will be flushing all the hoses, evaporator and condenser. Basically flushing everything except the replaced components and the compressor. Does anyone know how much freon should be in this system? Also how much oil should I add. Red Dot has a pretty good formula to follow for oil but not sure how much I should take off for residual oil in the compressor?

56wrench · Aug 27, 2021

If you are doing a complete flush, i would suggest removing the compressor and draining into a measuring cup then you will know what it had. Then you can add that amount of new oil back in. You can also look up your compressor make and model to see how much oil it is supposed to have and how that compares to the amount you drained out. The two amounts should be fairly close

workshoprat92 · Aug 27, 2021

56wrench said:
If you are doing a complete flush, i would suggest removing the compressor and draining into a measuring cup then you will know what it had. Then you can add that amount of new oil back in. You can also look up your compressor make and model to see how much oil it is supposed to have and how that compares to the amount you drained out. The two amounts should be fairly close

On one website it says my compessor should take 5 oz. That seems awfully high to me for a rotary piston pump.

56wrench · Aug 27, 2021

Is that the axial piston compressor( sanden or sankyo)? 5oz seems a bit high but maybe not. I'm not home for a few days so i can't check my manuals. How much did you drain out?

workshoprat92 · Aug 27, 2021

56wrench said:
Is that the axial piston compressor( sanden or sankyo)? 5oz seems a bit high but maybe not. I'm not home for a few days so i can't check my manuals. How much did you drain
out?

I do not have the system open yet. I am wanting to do it this weekend but have all the information at hand so I can get this back together and be ready to go Monday. Attached is a link to the compressor. I am not sure if 5 oz is what it requires or just what it comes with. I cannot find anything anywhere on a 1988 FLC air conditioner capacities. I can find some info for an FLD of a newer model. It says the FLD takes 3 lb of freon and 9 oz of oil. I don't know how comparative that is to the FLC system.

https://www.coolairparts.com/AC-COM...-43555075-488-45075-ABP-N83-304049Q-QP15-1168

Truck Shop · Aug 27, 2021

It's actually pretty close but no two systems ever seem to be the same with Freightliner.
From one to the next even in same years. You have to remember some info is with or
without sleeper, with sleeper most are 4.6 lbs.-day cabs 3 lbs. IIRC

workshoprat92 · Aug 27, 2021

Truck Shop said:
It's actually pretty close but no two systems ever seem to be the same with Freightliner.
From one to the next even in same years. You have to remember some info is with or
without sleeper, with sleeper most are 4.6 lbs.-day cabs 3 lbs. IIRC

This truck has no sleeper. Even if did it wouldn't matter on this model. The flc's had two dans under the dash and one was ducted to the sleeper. It did not have a separate fan and evaporator in the sleeper. I think they started doing separate units when they went to the fld model but i could be wrong.

Truck Shop · Aug 27, 2021

Bunk A/C was a spec option, could be ordered with or without. That option doesn't exist these days.

Birken Vogt · Aug 27, 2021

Some compressors have a dipstick. Although I am not sure if they had them in 1988. The trouble is that the instructions said you had to charge run the system normally and then evacuate it and see how much oil was in the compressor and make adjustments from there. There were different levels depending on how far off vertical the dipstick was mounted. It could also be completely horizontal in which case it was useless. Probably trivia but it might help you. I probably have a manual in my computer if this is the case. I believe Sanden SD series.

workshoprat92 · Sep 4, 2021

Well finally got all the parts so I tore into it today. Removed the evaporator coil and cleaned it up. Akso flushed it out. Cleaned heater core and washed the air box it all sets in. Reinstalled with new expansion valve. Flushed all the lines and condenser coil. Replaced the receiver dryer and and the trinary switch.
Got it all back together and sucked it down for a good hour. Put 3lbs of freon and 6 oz of oil in it. So far it does not seem to cool any better than it did before. Mylow side pressure is aboit 10psi and high side us about 175 all at 85degrees outside air temperature. My damn fan runs all the time and wont shut off. The fan circuit in the trinary switch is open! Called freightliner and they say the fan circuit is supposed to be normally closed. My old switch that circuit is closed. Looks like I have a damn defective switch! Started raining its ass off before i could look into it further so I called it a day.

Does my pressures at 85 degrees look right? 175 high side seems a little low. Maybe not?

Birken Vogt · Sep 4, 2021

You need to put a digital thermocouple thermometer on the liquid line that exits the condensor. I try to find some metal that is convenient and insulate it with some foam or something. You want the temperature of that line to be about 10 degrees less than what the high side pressure is indicating and that is your subcooling. It means the last few turns of the condensor are full of liquid that is getting a little extra cooling before it leaves. If it has a sight glass, this can also help, but the high accuracy thermometer is what tells the tale really.

terex herder · Sep 5, 2021

That left the factory as an R12 system. Are you using R12 or 134? Conversions are hit and miss IME. Low side seems low and likely to freeze evaporator.

workshoprat92 · Sep 5, 2021

terex herder said:
That left the factory as an R12 system. Are you using R12 or 134? Conversions are hit and miss IME. Low side seems low and likely to freeze evaporator.

workshoprat92 · Sep 5, 2021

I agree the low side seems pretty low. I have not had a chance to get back at it. The evaporator was developing some ice but the air coming out of the vents dont seem real cold to me. I need to get a thermometer in the vent and check it.

It also had occurred to me that it just may be a system that does not convert well to 134 from r12. Being an 88 model it had to be factory r12. If thats the case it may be a waste of time and money better spent on a red dot back wall unit!

New expansion valve, new reciever dryer, new trinary switch which is fkn defective! All the lines are good and i know the evaporator is not plugged. Despite the trinary switch it should blow cold as all get out. Only thing left is the condenser which dies not look Stellar! And the compressor which i have a hard time believing it would be bad if it will pump 175psi and pull down to 10 psi.

workshoprat92 · Sep 5, 2021

Birken Vogt said:
You need to put a digital thermocouple thermometer on the liquid line that exits the condensor. I try to find some metal that is convenient and insulate it with some foam or something. You want the temperature of that line to be about 10 degrees less than what the high side pressure is indicating and that is your subcooling. It means the last few turns of the condensor are full of liquid that is getting a little extra cooling before it leaves. If it has a sight glass, this can also help, but the high accuracy thermometer is what tells the tale really.

I dont know im following you. Are you saying if my high side pressure Is 175 then my condenser outlet should be about 165 degrees? I dont know what temp uts at but its just luke warm to the touch. Really so is the inlet!

Birken Vogt · Sep 6, 2021

Download a pressure/temperature chart. But there should also be a temp scale on your high side gauge.

If the pressure is 175, then the saturation temperature (the majority of the condenser) should be 121 F. 10 degrees of subcool and the liquid leaving the cond should be 111F. So get the system running with the cab a reasonable temperature on recirc full fan, get the fan clutch on, RPM at 1100 or so and add charge slowly until your subcool is about 10F. This is the gold standard for charging if the calibrated weight is not available, or if they got it wrong.

It would be nice if they had sold you a 134A ex valve. Usually that's what you get these days.

As for freezing, there should be a temp probe hooked to a switch to disengage the compressor temporarily as the evap gets below freezing. Usually this only happens on lower fan speeds.

It sounds like you need to add charge but I always do it by the subcool method, it is directly measuring what you need to be measuring, but it needs a thermocouple, no point and shoot thermometer for me on this one.

workshoprat92 · Sep 6, 2021

Birken Vogt said:
Download a pressure/temperature chart. But there should also be a temp scale on your high side gauge.

If the pressure is 175, then the saturation temperature (the majority of the condenser) should be 121 F. 10 degrees of subcool and the liquid leaving the cond should be 111F. So get the system running with the cab a reasonable temperature on recirc full fan, get the fan clutch on, RPM at 1100 or so and add charge slowly until your subcool is about 10F. This is the gold standard for charging if the calibrated weight is not available, or if they got it wrong.

It would be nice if they had sold you a 134A ex valve. Usually that's what you get these days.

As for freezing, there should be a temp probe hooked to a switch to disengage the compressor temporarily as the evap gets below freezing. Usually this only happens on lower fan speeds.

It sounds like you need to add charge but I always do it by the subcool method, it is directly measuring what you need to be measuring, but it needs a thermocouple, no point and shoot thermometer for me on this one.

Ok I think I get what you are saying. The valve they sold me when I look up the part number does show it to be a 134a valve.

From what I see of the chart I am probably low on charge. I have already put 3 lbs in this system. 4 12oz cans. I didn't get a soec from freightliner as this truck is old and no one there seems to know or how to find out for sure! I have a hard time believing it would take more than 3 lbs but I suppose it could.

I need to solve my trinary switch issue before I add more freon. I am going to have to pull the system down to replace the defective new part! Its the kind that does not have a Schrader valve! Also i think when I pull it down I need to go ahead and change my condenser. The find are fairly well screwed. I used a fin comb but it's still pretty ugly.

Birken Vogt · Sep 6, 2021

Replacing the condensor good. Hope you don't regret leaving the compressor, if it fails it is going to blow chunks into the new condensor.

The idea with the subcool method is to be able to measure when the bottom of the condensor is starting to get full of liquid. And then add a bit more until you have some excess liquid down there. The numbers tell the story as it goes.

When you do it this way you know it is right. But I prefer to do the measurements under the right conditions, cab 80-90F recirculate windows mostly closed (so it does not suck in hot engine air from the cowl), ambient temp 90F or better (so it's a good test but not so hot I'll melt standing next to the engine), fan locked on, engine at medium speed, and supply air to the condensor that is not getting recirculated from the radiator or engine however that works out for you. Sometimes nose into the wind, sometimes a big fan or sometimes nothing at all.

workshoprat92 · Sep 6, 2021

Yea toast!

workshoprat92 · Sep 6, 2021

Birken Vogt said:
Replacing the condensor good. Hope you don't regret leaving the compressor, if it fails it is going to blow chunks into the new condenser.

I just hate shot gunning part I dont know are bad. I guess from a preventative standpoint you are probably right since the condensor Is $309 aftermarket and $585 from freightliner! The compressor is only$207 from freightliner!

1988 FL freightliner air conditioning q1

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